PEROXIDE TREATMENT PROCESS

Abstract: A process for purification of hydrogen peroxide, the process including providing a source of crude aqueous hydrogen peroxide including organic contaminants; introducing the aqueous hydrogen peroxide into a separation means which includes at least one hydrocyclone; and collecting the purified hydrogen peroxide therefrom.

Description: PEROXIDE TREATMENT PROCESS The invention relates to a process for the purification of hydrogen peroxide and to an apparatus for production of purified hydrogen peroxide. Hydrogen peroxide is a clear, colourless liquid with a slight pungent odour. It dissolves completely in water. When used, it has minimal environmental impact because it decomposes to only water and oxygen. Peroxide is an efficient oxidiser and bleaching agent, which makes it useful in many industrial processes. Peroxide is commonly sold to industry as solutions of 35%, 50%, 60% or 70% by weight in water (by comparison, peroxide sold in a pharmacy for domestic use is generally 3 to 5% by weight aqueous solution) . The major and fastest growing use of peroxide is bleaching of wood pulp, in the paper and pulp industry. It is particularly effective in the bleaching of high yield pulps to higher brightness. High yield pulping is becoming increasingly important in today's global economy and a significant factor in the development of the Australasian Pulping industry. Hydrogen peroxide is also growing in chemical pulping and waste paper repulping. In gold mining, peroxide is used to enhance bleaching and to destroy excess cyanide in the extraction process. The textile and wool industry relies on peroxide to bleach many products. Many chemicals and plastics are made using peroxide in the production process. In waste water treatment, peroxide reduces odour in sewerage streams. The food industry employs peroxide to sterilise packaging materials and to bleach certain foods. It is known in the prior art to produce hydrogen peroxide by autoxidation of an organic compound such as anthraquinones, isopropyl alcohol or hydrazobenzene. In the case of anthraquinones such as 2-alkylanthraquinone the process involves a preliminary step of catalytic reduction. The anthraquinone is dissolved in an organic solvent and is hydrogenated using a catalyts to produce the corresponding anthraquinol which is then oxidized with oxygen, typically simply by aerating the mixture, to form the anthraquinone and simultaneously produce hydrogen peroxide. The anthraquinone is commonly called the reaction carrier or working material whereas the organic mixture of the anthraquinone and solvent in which the hydrogen peroxide is formed is known as the working solution. The hydrogen peroxide in the working solution is then extracted with water generally in an extractor vessel. Whilst such a process for preparing hydrogen peroxide is efficient, the hydrogen peroxide so formed does contain small, but significant, amounts of contaminants including organic contaminants remaining from the autoxidation process. It is known in the prior art to utilise various processing steps to improve the purity of the crude peroxide stream. However, such processes are highly expensive and significantly increase the cost of a new hydrogen peroxide manufacturing plant. The presence of organic contaminants in the hydrogen peroxide significantly reduce its stability and poses a significant safety risk. Contact between organic material and concentrated hydrogen peroxide, particularly at hydrogen peroxide concentrations of 50% by weight or more, poses a serious risk of fire or explosion. For many applicangs peroxide concentrations of 50 to 70% are desirable and are produced by vaporization of more dilute solutions. The safety risks posed by contamination are increased during vaporization and severely reduce the efficiency with which vaporization can be carried out. Typically the quality of hydrogen peroxide is measured in relation to pH, strength, turbidity, total carbon content, colour, smell and general apperance, such as the presence or otherwise of free floating material. It would be a significant advance in the art if a hydrogen peroxide could be produced of improved quality, but without the attendant costs and risks associated with the prior art. Accordingly it is an object of the present invention, to overcome, or at least alleviate, one or more of the difficulties related to the prior art. Accordingly, in a first aspect of the present invention there is provided a process for the purification of aqueous hydrogen peroxide, which process includes providing a source of crude hydrogen peroxide including organic contaminants; introducing the hydrogen peroxide into a separation means wherein the separation means includes at least one hydrocyclone; and collecting a purified hydrogen peroxide product therefrom. The source of hydrogen peroxide may be an aqueous solution of hydrogen peroxide from an extractor vessel. The extractor vessel may typically be a sieve plate type liquid extraction column. In the extractor vessel, a distribution co-efficient in favour of the aqueous phase allows the hydrogen peroxide to be concentrated, typically to a concentration of approximately 25% to 45% in the aqueous phase. The aqueous solution of hydrogen peroxide may be collected from the bottom of the extractor vessel. The aqueous solution of hydrogen peroxide may contain small amounts of entrained working solution, including organic contaminants, as well as other contaminants including non-organic contaminants. In a preferred embodiment the invention is utilized in purification of peroxide manufactured by autoxidation, particularly autoxidation of an anthraquinone. In this embodiment the contaminants will generally be derived from the working solution and may include an anthraquinone and an organic solvent in which the anthraquinone is preferably soluble and which solvent is typically water immiscible. The working liquor may then be extracted with water following the autoxidation process to provide the crude aqueous hydrogen peroxide which is introduced to the hydrocyclone. Typical examples of organic solvents used in the working solution are hydrocarbons such as distillate or kerosene. The separation means includes a hydrocyclone. Typical hydrocyclones are described in Australian Patent Numbers 521482 and 559530, the entire disclosures of which are incorporated herein by reference. The hydrocyclones may be typically conocylindrical bodies in which the mixture to be separated is fed tangentially, preferably with an involute inlet, under pressure to create a vortex resulting in separation of components of the mix via an underflow and a light phase outlet of the hydrocyclone(s) (generally the overflow) . The hydrocyclones according to this aspect of the present invention may be characterised by having a relatively large length to diameter ratio (L/D) , preferably in excess of approximately 10, and a relatively small overflow orifice to diameter ratio (Do/D) ratio, preferably less than approximately 0.2, wherein L is the length of the hydrocyclone, D is the major cyclone diameter and Do is the orifice diameter of the port by which the lighter contaminant is removed (ie the overflow orifice diameter) . Preferably this port is located towards the inlet end of the hydrocyclone. More preferably L/D is at least 15 and, although a wide range of ratios may be used a convenient upper limit is 30. More preferred Do/D ratios are in the range of from 0.01 to 0.1. The light organic phase contaminants removed from the hydrocyclone may be stored or redistributed via process units such as vessels, pumps etc. Typically the light organic phase flow is less than approximately 10% of the total feed volume, more typically less than approximately 5% more preferably less than 3%. Preferably at least 0.5% of the total feed will be light organic phase. Such hydrocyclones are particularly useful in removal of small residual organic materials, for example working solution, which may be free phase or dissolved, as well as removal of other non-organic contaminants. Such hydrocyclone systems are particularly applicable for the removal of small amounts of lower density material from a continuous aqueous phase. For example, the concentration by volume of such light contaminant material may be less than approximately 2%, more typically less than approximately 100 ppm by volume. Such contaminants may further include small amounts of gas and solids present in the aqueous phase. It has been found that separation of contaminants using the hydrocyclone is particularly efficient when the crude hydrogen peroxide is introduced to the hydrocyclone at a temperature of 20 to 50°C and more preferably 30 to 50°C. Increases of as little as 10°C within the range 20 to 50° can result in as much as a 25-30% improvement in contaminant removal. The hydrocyclones may be placed in the crude peroxide stream at any point between the extractor outlet to the final storage tank prior to shipment or further treatment. The separation means preferably includes a plurality of hydrocyclones which may be arranged in parallel, the crude hydrogen peroxide feed being split using a manifold. Alternatively or in addition to using hydrocyclones in parallel two or more hydrocyclones may be arranged in series. Two types of series are possible. In the preferred type of series the contaminant depleted underflow of one or more hydrocyclones, containing primarily an aqueous phase, is fed into one or more secondary cyclone to provide further removal of contaminants. In the alternative type of series the contaminant enriched overflow of one or more hydrocyclones is fed into one or more secondary cyclones for further separation of aqueous hydrogen peroxide from the organic phase. Additional process units or items of equipment may be placed upstream, downstream, or in parallel with the hydrocyclones to facilitate enhancement of the quality of the hydrogen peroxide. Enhanced quality includes reduced total carbon (TC) , lower turbidity, lighter colour, increased stability, consistency and less odour. In a further aspect of the invention there is provided an apparatus for treating crude aqueous hydrogen peroxide comprising organic contaminants the apparatus including a seive plate solvent extraction column and at least one hydrocyclone to which the aqueous phase from the extraction column is fed. The present invention will now be more fully described with reference to the accompanying drawings and examples. It should be understood, however, that the description following is illustrative only and should not be taken in any way as a restriction on the generality of the invention described above. Figure 1 is a flow chart illustrating a process and apparatus for the purification of hydrogen peroxide according to one embodiment of the present invention. Figure 2 is a flow chart illustrating a process and apparatus for purification of hydrogen peroxide according to another embodiment of the invention. Hydrogen peroxide is formed in a mainly organic mixture commonly called a "working solution". In accordance with Figure 1 the working solution flows into an extractor vessel (1) via working solution inlet (2) towards the bottom of the extractor vessel (1). In the extractor, a distribution co-efficient in favour of the aqueous phase, which enters towards the top (4) of the extractor vessel, allows the hydrogen peroxide to be concentrated to typically 25% to 45% in the aqueous phase. This extraction of hydrogen peroxide from the working solution into the aqueous phase is done in the extractor vessel which is typically a sieve plate liquid extraction column. Towards the top of the extractor vessel the working solution, with some entrained aqueous phase but depleted of hydrogen peroxide, leaves the extractor vessel via working solution outlet (3) . Towards the bottom of the extractor vessel the aqueous phase, now concentrated with hydrogen peroxide but containing some small amounts of entrained working solution and other contaminants, leaves the extractor vessel via aqueous phase outlet (5). This stream is often referred to as a "crude peroxide stream". This crude peroxide stream is then subject to one or more further process steps. These process steps are prior to the crude peroxide stream being concentrated and/or stabilised and stored ready for shipment. The aim of the steps is to remove small residual organic material (e.g. working solution) which may be free phase or dissolved; and also, these steps may remove other non-organic contaminants. The crude peroxide stream (5) is fed preferably via a pump and/or a primary separator (6) to a hydrocyclone (7). The crude peroxide stream (5) is fed tangentially into the hydrocyclone (7) which has an involute inlet and dimensions listed in Example 1 below to produce an underflow (7a) which is an aqueous hydrogen peroxide stream reduced in organic contaminants and an overflow stream (7b) which is enriched in organic contaminants. The apparatus may be provided with a line (8) for bypassing the hydrocyclone which bypass line (8) may include one or more parallel treatment means (9) for separation of contaminants. The underflow (7a), in addition to any by-pass line feed (10), is fed to a storage vessel (11). The purified underflow stream of the hydrocyclone (7) may be provided with a recycle line (10) to allow recycle of a portion, preferably 10 to 70%, of the underflow for processing with the crude peroxide stream (5). A separation vessel (12) is provided for receiving the enriched organic phase of the hydrocyclone (7). The separation vessel (12) may allow gravity separation of organic and aqueous phases and be provided with means for recycling the aqueous phase to the crude peroxide stream. Referring to Figure 2 there is shown a further embodiment of a hydrogen peroxide purification apparatus comprising an extractor vessel (13) (as described with respect to the extractor vessel (1) of Figure 1), a solvent scrubber (15) for receiving crude aqueous hydrogen peroxide, a multiplicity of hydrocyclones (16) (preferably four hydrocyclones) arranged in parallel for receiving the crude aqueous phase from adjacent the base the scrubber (15) via transfer pump (17), organic crude recovery tank (18) for receiving the overflow from the hydrocyclones which overflow is enriched in the organic phase and a recycle line (19) for enabling a portion of the underflow of the hydrocyclones (7), which has reduced contamination, to be recycled and admixed with the crude hydrogen peroxide. Further downstream processing of the underflow is provided by an aqueous hydrogen peroxide filter (20) before the purified hydrogen peroxide is fed to a storage tank (29). The purified hydrogen peroxide may be concentrated in an evaporator (not shown) to provide a hydrogen peroxide concentration of 50-70% by weight. In the purification process the working solution containing hydrogen peroxide generated as a result of anthraquinone autoxidation in a hydrocarbon solvent is fed into the extractor (13) adjacent the bottom and fresh water is introduced adjacent the top. Counter current extraction of the peroxide into the aqueous phase results in a crude hydrogen peroxide solution containing from 25 to 35% by weight of hydrogen peroxide which is fed from the bottom of the extractor (13) to a counter-current scrubber (15) adjacent the top. It is particularly preferred that the crude hydrogen peroxide line (14) is provided with a heat exchanger (21) which maintains a temperature in the range of about 30 to 45°C. In contrast conventional hydrogen peroxide purification processes generally cool the crude peroxide stream to less than 20°C. The crude hydrogen peroxide line (14) may also be provided with a valve (14a) to regulate flow. Organic phase liquid, preferably a hydrocarbon, is introduced to a scrubber (15) toward the bottom so that counter current of the lighter organic phase and aqueous phase results in partial extraction of impurities from the aqueous phase. The aqueous hydrogen peroxide phase is fed from adjacent the bottom of the counter current scrubber (15) to hydrocyclones (16) via a pump (17). The hydrocyclones are arranged in parallel and crude hydrogen peroxide is introduced via manifold (22) . The dimensions of the hydrocyclones are preferably as described in Example 1 below. The overflows of the hydrocyclones (16) are combined in overflow outlet manifold (23) and fed to organic crude recovery tank (18) which allows the aqueous and organic phases to separate. The aqueous phase which separates in the organic crude recovery tank (18) may be recycled from adjacent the base of the tank (18) via pump (24) and valve (25) to be mixed with the crude aqueous hydrogen peroxide in crude hydrogen peroxide line (14). The organic phase which separates in the organic crude recovery tank (18) may be delivered via an overflow (26) for reuse or further processing. The underflows of the hydrocyclones (16) are combined in underflow outlet manifold (27) and are fed to a filter unit (20) to remove at least part of any remaining traces of organic phase in the aqueous hydrogen peroxide. The filter unit (20) preferably includes glass wound filter elements. At least part of the underflow, preferably from 10 to 70%, from the hydrocyclones is recycled via recycle line (19) and combined with the crude aqueous hydrogen peroxide transferred from the solvent scrubber (15). The inclusion of a recycle has been found to significantly increase the efficiency of contaminant removal. The traces of oil removed at the filter (20) may be transferred to the organic crude recovery tank (18) via transfer time (28) . The purified aqueous hydrogen peroxide has a concentration of about 25 to 35% and may be fed to a storage tank and/or vaporized to further concentrate the hydrogen peroxide. The use of the hydrocyclones (16) significantly improve product quality by increasing the efficiency of removal of organic contaminants. As a result the product has high stability and concentration of the hydrogen peroxide may safely be carried out by vaporization of the purified product to provide a concentration of, for example from 50 to 70% by weight. The removal of contaminants improve the quality performance and marketability of the manufactured hydrogen peroxide. Some of the typical measures used to assess the quality of hydrogen peroxide include, pH, strength, turbidity, total carbon content, colour, smell and general appearance such as the presence or otherwise of free floating material. EXAMPLE 1 Test Hydrocyclone The test hydrocyclone had the following dimensions: D = 38 mm = Major hydrocyclone diameter Do = 1.5 mm = Orifices diameter for light phase unit L = 1016 mm = Hydrocyclone length Therefore L = 26.7 Do = 0.039 D D Test Configuration This configuration was as depicted in Figure 1 and there was no process units other than pump (6) between the feed to the hydrocyclone and the crude peroxide outlet (5). Bypass line (8) and recycle line (10) were not used so that all flow passed directly through the hydrocyclone (7) . The feed strength was approximately 35% with the temperature of about 45°C. Typical results were: Feed inlet to hydrocyclone : 16.4 NTU turbidity 211 mg/1 total carbon Treated outlet of hydrocarbon : 2.1 NTU turbidity 192 mg/1 total carbon (TC) The dissolved Total Carbon (TC) was 176 mg/1. The hydrocyclone was operated with a light phase flow of less than 3% of the total feed flow to the hydrocyclone. The process according to the present invention thus results in a reduction in total carbon (TC) of approximately 54%. EXAMPLES 2 AND 3 Test Hydrocyclones Primary dimensions as for the test program. Test Configuration For this test configuration there was 3 main process units upstream of the hydrocyclone. There was a packed solvent scrubbing vessel of the type described with respect to Figure 2 [solvent scrubber (15)]; a further vessel to allow gravity separation of organic solvent * immediately downstream of the solvent scrubber and a process pump to feed the hydrocyclone and final filter. Typical results were: Feed inlet to hydrocyclone _ : 45.5 turbidity (NTU) 220 mg/1 total carbon Treated outlet at 9 typically : 0.7 turbidity (NTU) 163 mg/1 total carbon The dissolved TC was 145 mg/1. The process according to the present invention thus results in a reduction in total carbon (TC) of approximately 76%. Finally, it is to be understood that various other modifications and/or alterations may be made without departing from the spirit of the present invention as outlined herein.

Claims: CLAIMS 1. A process for purification of hydrogen peroxide the process including providing a source of crude aqueous hydrogen peroxide including organic contaminants; introducing the aqueous hydrogen peroxide into a separation means which includes at least one hydrocyclone; and collecting the purified hydrogen peroxide therefrom. 2. A process according to claim 1 wherein the contaminants include an organic solvent which is lighter than water and wherein the process includes collecting the purified hydrogen peroxide from the underflow stream of the hydrocyclone and collecting contaminant enriched stream from the overflow of the hydrocyclone. 3. A process according to claim 1 wherein the process includes preparing crude hydrogen peroxide by autoxidation of a working solution including an anthraquinone and an organic solvent to produce hydrogen peroxide and extracting the working solution with water to provide an aqueous hydrogen peroxide composition containing organic contaminants. 4. A process according to claim 1 wherein the separation means includes a plurality of hydrocyclones and the crude aqueous hydrogen peroxide is introduced to the plurality hydrocyclones by parallel feed. 5. A process according to claim 2 wherein a portion of the underflow of the hydrocyclone is recycled and combined with the aqueous hydrogen peroxide upstream of the hydrocyclone. 6. A process according to claim 1 wherein the crude aqueous hydrogen peroxide is introduced to the hydrocyclone at a temperature in the range of from 30° to 50 ° . 7. A process according to claim 1 wherein the hydrocyclone has a length to major diameter ratio (L/D) in excess of 10 and the ratio of the diameter of the overflow orifice to the major hydrocyclose diameter (Do/D is less than 0.2. 8. A process according to claim 1 wherein the concentration of hydrogen peroxide in the crude hydrogen peroxide is in the range of from 25 to 45% by weight. 9. A process according to claim 2 wherein the total light phase flow of the hydrogen peroxide from the hydrocyclone is less than 10% by volume of the total feed of the hydrocyclone and the contaminant material constititutes less than 2% by volume of the total feed. 10. A process according to claim 2 which comprises feeding the overflow of the hydrocyclone to a separation vessel, separating the overflow into aqueous and organic phases in the separation vessel and recycling the aqueous phase to a point upstream of the hydrocyclone. 11. A process according to claim 1 or claim 3 wherein the crude aqueous hydrogen peroxide is extracted with an organic solvent prior to introducing the aqueous hydrogen peroxide to the hydrocyclone. 12. An apparatus for treating crude aqueous hydrogen peroxide including organic contaminants the apparatus including a seive plate solvent extraction column for counter current extraction with an organic solvent and at least one hydrocyclone to which the aqueous phase from the extraction column is fed. 13. An apparatus according to claim 12 wherein the underflow outlet of the hydrocyclone is provided with a transfer line for providing recycle of a portion of the underflow to a point upstream of the hydrocyclone. 14. An apparatus according to claim 11 wherein the hydrocyclone has a length to major diameter ratio (L/D) in excess of 10 and the ratio of the diameter of the overflow orifice to the major hydrocyclone diameter (Do/D) is less than 0.2.

Inventors: COLLINS PAUL JAMES, HUMPHRIES PAUL BRADLEY, PRENDERGAST GAVAN JAMES JOSEPH, COLLINS, PAUL, JAMES, HUMPHRIES, PAUL, BRADLEY, PRENDERGAST, GAVAN, JAMES, JOSEPH
Applicants: COLLINS PAUL JAMES, DU PONT AUSTRALIA, HUMPHRIES PAUL BRADLEY, PRENDERGAST GAVAN JAMES JOSEPH, COLLINS, PAUL, JAMES, DU PONT (AUSTRALIA) LTD., HUMPHRIES, PAUL, BRADLEY, PRENDERGAST, GAVAN, JAMES, JOSEPH
Application year: 1994
Main classification: C01B15
IPC codes: B01D11, B04C5, B04C7, C01B15